Skip to Content

Hydralazine: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 22, 2019.

1. How it works

  • Hydralazine is a vasodilator - this means it relaxes smooth muscle inside blood vessels, making the blood vessels wider, and allowing more blood to flow through. This reduces how much force the heart has to exert to pump blood through the blood vessels, and reduces blood pressure.
  • Experts aren't sure exactly how hydralazine does this, but suggest it may alter calcium movements through muscle which affects how much the muscle contracts.
  • Hydralazine belongs to the class of medicines known as vasodilators.

2. Upsides

  • Used for the treatment of high blood pressure (BP), either alone or in combination with other agents.
  • Available as oral tablets or in an injectable form. The injectable form of hydralazine may be used by healthcare providers when there is an urgent need to lower blood pressure or if the oral tablets cannot be given.
  • Hydralazine also improves blood flow to the outer extremities (such as the fingers and toes), increases heart rate and the volume of blood pumped with each heartbeat, and overall heart performance.
  • More effective at reducing diastolic (the bottom number of a BP reading) rather than systolic (the top number of a BP reading) blood pressure.
  • Less likely to cause a drop in blood pressure on standing (postural hypotension) as it preferentially targets arteries rather than veins.
  • In people with high blood pressure and healthy kidneys, hydralazine tends to increase blood flow through the kidneys, improving kidney function. However, it should be used with caution in people with advanced kidney damage.
  • Hydralazine oral tablets are only available as a generic.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • A headache, nausea, vomiting, diarrhea, heart palpitations, and weight loss. Less common side effects include constipation, dizziness, shortness of breath, changes in blood counts, nasal congestion, and flushing.
  • Because hydralazine stimulates cardiac muscle, it may cause chest pain, angina attacks, and ECG changes. Associated with a higher risk of heart attack; therefore, should not be used in people with coronary artery disease.
  • May not be suitable for some people including those with a history of stroke or rheumatic heart disease.
  • May cause damage to peripheral nerves, leading to weakness, numbness and pain in the hands and feet. Addition of pyridoxine (vitamin B6) may help.
  • Hydralazine is one of the most common drugs implicated in Drug-induced Systemic Lupus Erythematosus (DILE). Symptoms may occur anywhere from three weeks to two years after taking hydralazine and include rash, fever, weight loss, fatigue, joint or muscle pain, and kidney inflammation. Seek urgent medical advice if this occurs.
  • May interact with some drugs including MAOI antidepressants and other antihypertensives.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Hydralazine lowers blood pressure but also stimulates the heart which may increase the heart rate and lead to angina symptoms. Hydralazine is one of the most common drugs associated with drug-induced systemic lupus erythematosus (DILE).

5. Tips

  • May be taken with or without food, but should be taken consistently either with or without food. Food may increase the blood levels of hydralazine, increasing the risk of side effects such as a blood pressure drop when standing.
  • Be cautious driving or performing tasks that require concentration if hydralazine makes you dizzy. Also be careful when going from a sitting or lying down to a standing position. Alcohol, dehydration, exercise, or illness may exacerbate these effects.
  • Tell your doctor if you experience any chest pain or heart palpitations while taking hydralazine.
  • Seek urgent medical advice if you develop a rash, fever, joint or muscle pain, difficulty breathing, or numbness or nerve pain in your hands or feet.
  • Talk to your doctor or pharmacist before buying other medications over the counter to check that they are compatible with hydralazine.

6. Response and Effectiveness

  • Peak blood levels of hydralazine are usually reached one to two hours after oral hydralazine; sooner if injectable hydralazine is used.
  • The maximal blood pressure lowering effect is seen 10 to 80 minutes after hydralazine injection; data is not available regarding peak blood pressure lowering effects of the tablets.
  • Effects are short-lasting, necessitating a four-times daily dosing regimen.

7. Interactions

Medicines that interact with hydralazine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with hydralazine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with hydralazine include:

  • amphetamines, such as dexamphetamine
  • antipsychotics, such as haloperidol or thioridazine
  • diazoxide
  • duloxetine
  • levodopa
  • methylphenidate
  • monoamine oxidase inhibitors, such as isocarboxazid or phenelzine
  • NSAIDs such as diclofenac or ibuprofen
  • other vasodilators, such as nitroglycerin
  • pholcodine
  • phosphodiesterase 5 inhibitors, such as sildenafil and tadalafil
  • selegiline.

Note that this list is not all-inclusive and includes only common medications that may interact with hydralazine. You should refer to the prescribing information for hydralazine for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use hydralazine only for the indication prescribed.

Copyright 1996-2021 Revision date: November 21, 2019.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.